Warning, LONG post! I thought this was an appropriate place to put it. I attended a mini-symposium at NC State last night that was on DSLD and featured the Chief Medical Officer and Director of Equine Programs at Univ of GA (Dr. Mueller), and Pathology professor and MD, Dr. Halper. She is the one who discovered that DSLD horses have increased proteoglycans in their tendons and developed the staining technique that uncovers this. She is an expert in tendons and ligaments, not horses. Please let me know if you have any questions, this is an abbreviated summary:
DSLD notes!
From NC State Symposium with Dr. Halper (MD, Ph.D., pathologist) and Dr. Mueller (DVM, Ph.D – equine surgeon)
Dr. Mueller :
He said the onset of DSLD is usually from foals to 5-6 years of age, although it can show up in older horses. The biggest differential diagnosis is traumatic injury or desmitis from regular work. He sees subclinical desmitis all the time in sport horses, and he usually sees a mix of signs of desmitis and DSLD when looking at DSLD horses in work.
He believes ultrasound can often be a useful diagnostic because DSLD presents WITHOUT core lesions or acute inflammation because it is chronic. (showed ultrasounds) The ligaments are enlarged, but not very painful because the ligaments have more ground substance/proteoglycans between the fibers that have built up over time. As horses age, they accumulate more proteoglycans and therefore age is important in the reading of any histological tests.
He stressed that the nuchal ligament staining is not a perfect correlation. NOT a perfect correlation. It does not correlate with extent of disease. It’s subjective. NOT ALL, but most horses with significant proteoglycan accumulation can develop the syndrome. It’s the most predictive, least invasive ligament to biopsy in working horses that they have come up with.
Veterinarians often get the wrong tissue on biopsy, and often go too high in the crest. Vets use needle biopsies, core biopsies, and other insufficient techniques. He makes a vertical cut, about 2-3 inches, then dissects down to the ligament and visualizes it. He uses Kelley hemostats to isolate about an inch of ligament, then cuts dorsal and caudal to that, so the ligament is attached to the forceps. He then closes the would and gives one shot of penicillin. His incisions close nicely, and he always makes them on the side the mane falls on so any scar will be covered. His scars heal well. He is a surgeon… He is happy to talk to vets prior to biopsy about technique.
Major decisions, such as euthanasia or breeding, CANNOT- be made on biopsy results, he stressed. The whole horse presentation must be used in evaluating the condition. It is not a condition of the suspensory ligaments, it affects the whole horse. It is likely a syndrome.
There’s no treatment for the condition. Shock wave therapy, stem cell therapy won’t work. The degeneration will continue. He knows an ambiguous result is very hard on clients and talks to them regularly. Shoeing changes can make a horse more comfortable, and he showed shoes that can keep a fetlock from rubbing the ground (<shudder>).
An NC State vet said he is seeing a sharp increase in Warmbloods but doesn’t know why.
Dr. Halper talked about the study and histology techniques she uses to identify what is probably a defect in an enzyme that regulates proteoglycans.
She said horses have more collagen in their arteries than humans. The DSLD horses had definite changes in cardiomyocytes, aortic smooth muscle and other cells – the effect is unknown. Friesians can exhibit cardiovascular mortality with DSLD, but they only have anecdotal evidence as the only horses they’ve seen this happen in are Fresians. Low n size.
She has done some genetic work (next generation sequencing) to look at upregulation/downregulation of genes with DSLD, but it is expensive and hard to get tissue from horses (she uses a skin biopsy, but funding is a real issue to continue the work). Plus, I know that the published genetic sequence is from one breed (don’t know what it is) and there’s a TON of variability in horse breeds. What are normal splice variants or expression of any equine gene? She is trying to get funding from horse-specific sources, too.
I talked to them both individually for some time, and they are both very cognizant of how difficult it is for owners to get only a probability from the nuchal ligament result. But since they have seen false positives, they DO NOT want an owner to give up on their horse if the test is the ONLY piece of data. Again, they stressed that the vet’s responsibility is to look at the whole horse, and Dr. Mueller indicated that sometimes, the vet has no idea and throws out the biopsy idea.